Liquid crystal display matrix array employing ovonic threshold switching devices to isolate individual pixels

ABSTRACT

An acute matrix liquid crystal display panel including 1) a plurality of liquid crystal display elements distributed in a matrix of rows and columns; 2) means for supplying video signals and display element selection signals, including row and column conductors; and 3) a plurality of paired Ovonic threshold switches and resistive elements each serially coupled between the corresponding row or column conductor and the liquid crystal display element, the Ovonic threshold switches acting as display element selection devices and current isolation devices in which the Ovonic threshold switches having an off state resistance of at least 1×10 9  ohms.

This application is a continuation-in-part of U.S. Ser. No. 08/324,071filed Oct. 14, 1994.

FIELD OF THE INVENTION

This invention relates generally to liquid crystal type informationdisplay arrays. Specifically, this invention is directed to using Ovonicthreshold switching devices employing novel chalcogen thresholdswitching materials in series with a resistive element as electricalisolation devices in liquid crystal display arrays. The Ovonic thresholdswitches allow for energizing and de-energizing discrete selected pixelson the array without influencing other non-selected pixels on the array.

BACKGROUND OF THE INVENTION

The present invention pertains to image-display panels. Moreparticularly, it relates to large-area, high-density, liquid-crystalimage-display panels for use in television systems and the like. Sinceat least as early as the cathode-ray tube, much effort has been devotedto the ultimate objective of a flat image display panel. Flat-paneldisplay devices have included matrices of such devices aselectroluminescent cells, mechanical shutters, orientable particlessuspended in a medium, radiation-emitting diodes, gas cells and liquidcrystals.

Most prior flat-panel displays have employed a matrix of crossedconductors. The application of a potential between a given verticalconductor (a "column conductor") and a given horizontal conductor (a"row conductor") results in actuation of a light-display elementsituated at the crossing of those two conductors. In order to insureagainst even partial energization of display element located elsewherealong either one of the row and column conductors, each display elementis associated with a selection or isolation device that typically takesthe form of a series diode or transistor having a non-linearcharacteristic. A selecting potential biases the selection device toapproximately the threshold of its characteristic and the videomodulating voltage raises the applied potential beyond the threshold ofthat curve.

For addressing such prior panels, numerous different sources have beensuggested. These include the use of commutators, shift registers,traveling-wave pulses, and similar techniques. However, the degree ofsuccess obtained had been substantially less than that required, forexample, in the case of displaying conventional television pictures.

U.S. Pat. No. 3,765,011 to Sawyer, et al. discloses an image-displaypanel that offered advantages relative to the aforedescribed priorpanels of the same general nature. In the image-display panel of thatpatent, picture-element isolation was achieved by two-terminal Ovonicthreshold or breakdown-type switches that were coupled individually inseries with respective light-display elements distributed over the panelin a matrix defining horizontal rows and vertical columns. Differentcolumns of the switches were selectively addressed with pulses that, inconjunction with row-selection pulses, fired the switches. At the sametime, the different columns were also addressed withvideo-representative modulating pulses that corresponded individually tothe instantaneous level of the picture information. Finally, differentrows were addressed in a manner that supplied the voltage needed forfiring, in conjunction with the column firing pulses, and completedrespective return circuits for the firing pulses and the modulatingpulses.

While the Ovonic threshold switches of the past were adequate for thelow density displays of a bygone era, their properties are not adequatefor the higher density displays required today. Therefore, the interestof most display manufactures has since moved to other isolation devices.The threshold materials and the element designs of the prior artthreshold switches proved inadequate to handle the ever increasingdemands of large-area, high-density displays.

Today, large-area, high-density, liquid crystal displays (LCDs) havebecome a $4 billion per year market, which is expected to grow to $7billion in the next three years. The demand for higher display densityand better picture contrast continues to increase. Early displaysemployed a liquid crystal pressed between two glass plates withtransparent conductors. For low density displays this inexpensivetechnique was acceptable, but, using this technology, the picturecontrast reduces as the density increases and with today's displays,this technique is unusable.

A major problem facing LCD manufacturers is that each pixel must bebiased periodically to maintain its color. This is done by applying avoltage to a single addressing row of the display and an intensitysignal to the each of the addressing columns of the display. This biasesevery pixel along the row properly. If there are N rows, each pixel canonly be biased for one Nth of the time. The picture contrast roughlyscales with this time and rapidly diminishes to nothing as the number ofrows increases.

The solution is to provide a nonlinear conductor in the electrical pathto each pixel, such as a diode, which acts as an isolation device. Thepixel can be biased at a potential where the nonlinear element willconduct. When the pixel is not biased, the nonlinear element will notconduct, so the pixel will remain in the biased state. Liquid crystalmaterials have a very low conductivity and the display pixel act like0.2-0.4 pF capacitors. However, since no nonlinear conductor is ideal,charge leakage will occur.

Each pixel in an active matrix LCD display must contain an addressableswitching element which acts as a current isolation device. Manytechnologies have been used for this application. In evaluating themerits of various approaches, several parameters must be considered. Thefollowing list includes the 9 most important considerations.

1) The current drive capability of the switch must be high when it isswitched on. This allows the pixel to be switched in a very short time.As displays become more dense, there is less time for each row of pixelsto be switched.

2) The current leakage of the switch must be low when it is switchedoff. This prevents the charge from leaving the pixel in between thetimes when it is addressed. This is very important for gray scalecapability in a display. The requirement becomes more severe as thedisplay density increases.

3) The area of the switch must be subtracted from the area of eachpixel. This reduces the amount of light that can be projected throughthe pixel. It is desirable to have a small area switch to increase theaperture ratio of the pixel area.

4) If the switch has light sensitivity, a shadow mask is required toprevent light from reaching the device. This can add extra processingsteps and can reduce the aperture ratio.

5) Two terminals are necessary to address an array of pixels in adisplay. Some switching devices have three terminals and require threecontacts at each pixel location. This adds complexity to the mask andreduces the aperture ratio.

6) The cost of a display is directly related to the number of processingsteps in its manufacture. It is desirable to have the least possiblenumber of masking steps.

7) Portable computers are being proposed which use low voltage to reducebattery power. The voltage requirements of the display have been alimitation in making an all low voltage computer.

8) The switching speed of the device must be fast enough to notsignificantly affect the charging of the pixel. As display performancecontinues to increase the response time will become a more importantconsideration.

9) The processing temperature of the switch must be below the softeningpoint of the substrate. Corning 7059 glass, which is a preferredsubstrate, has a softening point of 450 ° C. Other substrates, whilehaving a greater softening or melting point, are much more expensive.

The following table compares these 9 considerations for a number ofprior art display technologies.

                                      TABLE 1                                     __________________________________________________________________________    Prior                                                                             On   Off                      Voltage                                                                           Response                                                                           Processing                         Art Current                                                                            Current                                                                            Aperture                                                                           Light                                                                              Terminals                                                                          Masking                                                                            Range                                                                             Time Temperature                        Devices                                                                           (A)  (A)  Ratio                                                                              Sensitivity                                                                        Required                                                                           Steps                                                                              (V) (ns) (°C.)                       __________________________________________________________________________    a-TFT                                                                             1 × 10.sup.-5                                                                1 × 10.sup.-12                                                               .3   YES  3    6    >12 3000 300                                p-TFT                                                                             1 × 10.sup.-5                                                                1 × 10.sup.-11                                                               .4   YES  3    6    >5  200  600                                MIM 1 × 10.sup.-6                                                                1 × 10.sup.-10                                                               .53  NO   2    3    >12 10000                                                                              300                                Diode                                                                             1 × 10.sup.-4                                                                1 × 10.sup.-12                                                               .4   YES  3    4    >12 5000 300                                OTS 1 × 10.sup.-3                                                                1 × 10.sup.-7                                                                .6   NO   2    3    >3  <1000                                                                              300                                __________________________________________________________________________

A fundamental problem with display technology today is finding anonlinear element with a suitable ratio of on current to off current.Because the display environment is noisy, the nonlinear isolationelement must have a sharp transition from the conducting to thenonconducting state.

Amorphous silicon thin film transistors, currently the most popularelement, have on to off ratios on the order of 10⁷. While improvementsin processing may, someday, increase this by another order of magnitude,the primary drawback of thin film transistors is that they must be verylarge to drive the necessary current in the on state. As displays arraysreach 1000 by 1000 pixels in size, these transistors are no longercapable of sourcing sufficient current to adequately bias a pixel. Also,the remainder of the consideration factors impose severe limitations onstate-of-the-art displays. Polycrystalline thin film transistors offer asolution to the biggest problems of amorphous thin film transistors,i.e. the inadequate current in the on state. They have a much greater oncurrent than an amorphous transistor, but their on to off ratio is notas good as their amorphous counterparts. They also require less area toproduce, so the aperture ratio is improved. Present techniques, however,require high temperature fabrication. This requires expensive substratesand makes the cost of large area displays prohibitive. Current,state-of-the-art, displays use this technology, and while improvementsmay be made, fabrication of displays using transistor isolation devicesis very complex. Polycrystalline transistors add 6 masking steps to adisplay fabrication process. This has a significant impact on yield.Current state of the art fabrication facilities have yields below 50%,making such displays very costly.

Metal-insulator-metal diodes offer a simpler layout than transistordisplays and are very easy to fabricate, thus allowing less expensivedisplays to be produced. They are the simplest method of employing anonlinear element into a display, so yields are significantly better.Unfortunately, the ratio of their on and off currents is not very high.These devices have a nonlinear characteristic which can provide up to 5orders of on to off ratio. This was sufficient for intermediate densitydisplays, but present displays require much lower leakage current thanthis technology can provide. This prohibits the use of this technologyin high density displays where both high on current and low off currentare vital.

Diode isolation is somewhat simpler than transistor isolation and diodesare nearly as easy to fabricate as MIM devices. Diode isolation offersexcellent on/off current ratios of about 8 orders of magnitude. However,a diode only conducts in one direction, thus making two diodes necessaryat each pixel. Therefore, each pixel must have two row contacts and acolumn contact. This is a 50% increase in the number of interconnectionsto the display, which has limited this technique's acceptance. Thus,while diodes offer an acceptable solution which has less masking stepsthan a TFT display, the cell complexity and number of contacts isincreased.

The prior art threshold switch offers all the desirable propertieslisted in this investigation except for off-state resistance. It has thehighest on current and the fastest response time, allowing a high enoughbandwidth for HDTV like applications. It has the widest aperture ratio,allowing better contrast and more energy efficient lighting. It is notlight sensitive and has the simplest device structure, allowing a lowercost display to be developed. The device can also be operated at a lowervoltage than any other technology, which will make it most desirable inbattery operated computers. The only thing it is lacking is a very lowoff current (or high off-state resistance), which would allow foraccurate gray scale performance.

The present invention discloses threshold switches and chalcogenidethreshold switching materials having all of the desirable properties ofthe prior art threshold switches and also having a very low off-statecurrent (high off-state resistance).

A display using threshold switches has the simplicity advantage of MIMdisplays, but offers a performance exceeding all other technologiesemployed. Displays for HDTV and future computer displays will requireover 4 million pixels. Current technologies can not easily meet therequirements for such displays. A chalcogenide threshold switch approachusing the novel threshold switching materials of the present inventionaffords the performance necessary and is easy enough to fabricate thathigh yields will result.

SUMMARY OF THE INVENTION

The present invention discloses an active matrix liquid crystal displaypanel including:

1) a plurality of liquid crystal display elements distributed in amatrix of rows and columns;

2) means for supplying video signals and display element selectionsignals, including row and column conductors; and

3) a plurality of threshold switching elements each serially coupledbetween the corresponding row or column conductor and the liquid crystaldisplay element, said threshold switching elements acting as displayelement selection devices and current isolation devices;

said threshold switching elements having an off state resistance of atleast 1×10⁹ ohms.

Preferably the off-state resistance of the threshold switches is greaterthan about 1×10¹⁰ ohms. More preferably the off-state resistance isgreater than about 1×10¹¹ ohms. Most preferably the off-state resistanceis greater than about 1×10¹² ohms. The threshold switching materials ofthe present invention may be formed from As-Te based chalcogenides andthey additionally include one or more elements such as Ge, Si, P and Se.

When needed, a resistive element may be added in series with the Ovonicthreshold switch to insure the liquid crystal display element isproperly charged before the current flowing through the threshold switchfalls below the holding current thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a liquid crystal diode (LCD)image-display matrix using Ovonic threshold switches as deviceselectors/isolation devices;

FIG. 2 is a schematic representation of a current-voltage plot for atypical threshold switching device;

FIG. 3 shows and alternative embodiment of the instant invention,wherein a resistive element is provided in series with the thresholdswitch to insure the liquid crystal display element is properly chargedbefore the current through the threshold switch falls below the holdingcurrent thereof; and

FIG. 4 shows a voltage versus time plot for a typical drive scheme forpixels of the instant display which incorporate a series resistance inconjunction with the threshold switch.

DETAILED DESCRIPTION OF THE INVENTION

A fundamental matrix 1 for a liquid-crystal display panel is illustratedin FIG. 1. A plurality of liquid-crystal light-display elements 2 aredistributed over the panel so as to define horizontal rows which areconnected by row conductors 4, 5, and 6 and vertical columns which areconnected by column conductors 7, 8 and 9. Individual terminals of eachdisplay element 2 are ultimately connected between the respectivehorizontal and vertical conductors that cross at the approximatelocation of the display element. An Ovonic threshold switch 3 isconnected in series with each display element 2 between the row andcolumn conductive lines. These Ovonic threshold switches act as currentisolation devices and display element selection devices.

When a potential exceeding the threshold value of the Ovonic thresholdswitch is impressed across crossed row and column conductors, the deviceconverts to its highly conductive state by a process well known in theart and exemplified by FIG. 2. Once in its highly conductive state theOvonic threshold switch 3 allows current to flow therethrough, whichcharges the liquid crystal display element 2. This charging current isabove the minimum holding current of the Ovonic threshold switch 3 andkeeps the switch in the conducting state. Once the display element 2 ischarged to the required video voltage, the current through the thresholdswitch 3 drops below the holding current and the threshold switch 3automatically reverts to its highly resistive state.

The element selection electrical pulses which convert the Ovonicthreshold switches 3 to their conductive state and the video signalpulses which charge the liquid crystal display elements 2 are suppliedby the line drivers and decoders. The drivers and decoders are shown as"black boxes" 10 and 11 which may be separate distinct units or may beprovided on-board the display panel. These line drivers, and well as theother display driver circuitry required to form a working display areconventional in the art and need not be discussed in detail herein.

In FIG. 1, display element 2 operates in as a light modulator. Intypical practice, the liquid crystal material is sandwiched betweenelectrodes spaced apart by on the order of 5 microns. When no electricfield is applied, the liquid crystal material polarizes light in linewith a polarization filter. However, when a potential is applied betweenits electrodes the polarization angle changes and blocks light. Changingthe field results in a change of brightness so that a gray scale isobtainable.

The prior art Ovonic threshold switches used in the display of U.S. Pat.No. 3,765,011 to Sawyer, et al. is of a kind described in an article byGeorge Sideris entitled "Transistors Face an Invisible Foe," and whichappeared in Electronics, pp. 191-195, Sep. 19, 1966. They were aredescribed in an article entitled "Amorphous-Semi-conductor Switching" byH. K. Henisch which appeared at pp. 30-41 of Scientific American forSeptember, 1969.

Sayer et al. describes the prior art Ovonic threshold switch they usedthroughout their display matrix as "simply be a small layer or dot of aglass-like material deposited upon an electrode of the associatedlight-display element." The Ovonic threshold switches employed by theinstant inventors are discrete thin-film devices produced byphotolithographic deposition techniques and are much smaller in size,potentially less than one micron across.

Threshold switches exhibit bi-stability in the sense that, once fired,each switch continues to pass current to the associated display elementuntil the current is interrupted or until it falls below a criticalvalue called a holding current.

The characteristics of the Ovonic threshold switch are shown in FIG. 2.The switch presents a high resistance for voltages below a thresholdlevel V_(l). When that voltage across a switch is exceeded, the switchbreaks down and conducts at a substantially constant voltage V_(c) ;when conducting, the switch exhibits a low impedance. When the currentthrough the switch falls below a holding current I_(h), the switchreverts to its high-impedance state; this occurs when the voltage acrossthe switch falls below the lesser level V_(c). The switching action isindependent of the polarity of the applied voltage, and switching inboth directions is rapid.

It is the off state resistance of the prior art Ovonic thresholdswitches which causes them to be inadequate for use as an isolationdevice in today's high-density, large-area liquid crystal displaypanels. This is true because the picture elements 2 will dischargethrough the prior art threshold switch even in the off state. Accordingto Sawyer et al, the "off" resistance of an ovonic switch may be of theorder of 10⁷ ohms. This is the reason that Sawyer, et al used anadditional capacitor in series with the liquid crystal display element.This additional capacitor helped to keep the display element charged asit lost its charge through the threshold switch due to its relativelylow off-state resistance.

The present inventors have fabricated new chalcogenide thresholdswitching materials having all of the desirable properties of the priorart materials, such as: high on-state current flow; low thresholdvoltage; light insensitivity; simple, low temperature production; highaperture ratio; two terminals; and fast switching times, andadditionally having a very high off-state resistance.

The off-state resistance of the Ovonic threshold switches of the presentinvention are on the order of at least 10⁹ ohms. Preferably theoff-state resistance of the threshold switches is greater than about1×10¹⁰ ohms. More preferably the off-state resistance is greater thanabout 1×10¹¹ ohms. Most preferably the off-state resistance is greaterthan about 1×10¹² ohms.

These materials are clearly superior to the prior art materials in theirability to isolate the display elements from the rest of the display andcause the display elements to retain their charge much longer than waspreviously possible.

The threshold switching materials of the present invention are As-Tebased chalcogenides. They additionally include elements such as Ge, Si,P, S and Se. One composition which is useful is As₄₁ Te₃₉ Ge₅ Si₁₄ P₁,wherein the subscripts are the atomic ratios of the respective elements.This basic material may be modified by substituting Se for either orboth of As and Te. Two examples of such a modified composition are As₃₈Te₃₇ Ge₅ Si₁₄ P₁ Se₅ and As₃₆ Te₃₄ Ge₅ Si₁₄ P₁ Se₁₀. In addition tomodification by substitution of Se, additional Si can be substituted foreither or both of As and Te. Examples of Si substitution are As₃₈ Te₃₇Ge₅ Si₁₉ P₁ and As₃₆ Te₃₄ Ge₅ Si₂₄ P₁.

Additional modifications to achieve extremely high off state resistancecan involve modification of the geometry of the body of thresholdswitching within the threshold switching device. For example, the crosssectional area and thickness of the body of threshold material many bemodified to increase or decrease the resistance of the threshold switchwithin certain limits.

In another embodiment (Shown in FIG. 3) a resistive element 12, such asa resistor, may be provided in series with each threshold switch 3 toinsure each liquid crystal display element 2 is properly charged beforethe current through the threshold switch 3 falls below the holdingcurrent thereof.

That is, since each liquid crystal display element (pixel) has a finitecapacitance and the resistance of the on-state threshold switch is verysmall the pixel takes very little time to charge (i.e. the circuit has avery small RC time constant). Therefore, the current flowing through thethreshold switch may fall below the holding current before the liquidcrystal display element has acquired a proper voltage. Therefore, todecrease the current flowing through threshold switch (i.e. slow thecharging of the pixel down) and allow all of the liquid crystal displayelements of a given row time to properly charge, it is sometimesadvantageous to include a resistive element in series with the thresholdswitch.

For example, a typical liquid crystal display element has a capacitanceof 0.2 pF, while the threshold switch has a typical capacitance of about10 fF and a holding current of about 0.1 microamps. For theseconditions, an in series resistance of about 10⁷ ohms is required toallow the liquid crystal display element to properly charge before thethreshold switch reverts to its non-conductive (or off) state.

Without the series resistances, the pixels would instantaneously chargeto an improper voltage. Description of a typical driving scheme for asingle pixel will help to illustrate the problem. First, a pixel drivingvoltage is applied to the pixel driving line (e.g. lines 7, 8 and 9)then a switching pulse is applied to the threshold switch driving line(e.g. lines 4, 5 and 6). As the voltage of the switching pulseincreases, the potential across the threshold switch increases until thethreshold voltage is reached at which time the threshold switch assumesits low resistance state. Nearly instantaneously, the liquid crystaldisplay element fully charges. However, the voltage to which the displayelement charges is not the correct voltage. This is because thethreshold switch reverts to its high resistivity state before theswitching pulse has discontinued. Therefore, the display element chargesto the additive value of the pixel driving voltage and whatever voltageof the switching pulse is at when threshold switch shuts off.

To alleviate this problem, the RC time constant of the circuit must beincreased dramatically. This allows the pixel to charge slower, thusproviding time for the switching pulse to finish before the thresholdswitch shuts off. Therefore, by including a series resistance, the RCtime constant of the circuit can be increased to the point that thepixel is still charging and the threshold switch is still in itsconductive state when the switching pulse ends. Thus, the final voltageapplied to the pixel will be proper.

FIG. 4 illustrates the drive scheme for the instant display utilizing aseries resistor. The top curve represents the switching pulse voltage(a.k.a. common driver voltage). The middle curve represents the appliedpixel driving voltage (a.k.a. segment driver voltage). Finally thebottom curve indicates the pixel voltage (or potential). As can be seen,using the series resistance allows the switching pulse to shut off longbefore the pixel reaches its final, proper voltage.

While particular embodiments of the present invention have been shownand described, it is apparent that changes and modifications may be madetherein without departing from the invention in its broader aspects. Theaim of the appended claims, therefore, is to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

We claim:
 1. An active matrix liquid crystal display panel including:aplurality of liquid crystal display elements distributed in a matrix ofrows and columns; means for supplying video signals and display elementselection signals, including row and column conductors; and a pluralityof paired Ovonic threshold switches and resistive elements each seriallycoupled between the corresponding row or column conductor and the liquidcrystal display element, said Ovonic threshold switches acting asdisplay element selection devices and current isolation devices; saidOvonic threshold switches having an off-state resistance of at least1×10⁹ ohms.
 2. The active matrix liquid display panel of claim 1, wheresaid Ovonic threshold switches have an off-state resistance of at least1×10¹⁰ ohms.
 3. The active matrix liquid crystal display panel of claim1, wherein said Ovonic threshold switches have an off-state resistanceof at least 1×10¹¹ ohms.
 4. The active matrix liquid crystal displaypanel of claim 1, wherein said Ovonic threshold switches have anoff-state resistance of at least 1×10¹² ohms.
 5. The active matrixliquid crystal display panel of claim 1, wherein said Ovonic thresholdswitches include a body of chalcogenide threshold switching materialdisposed between two electrical contacts.
 6. The active matrix liquidcrystal display panel of claim 5, wherein said body of chalcogenidethreshold switching material is a thin-film.
 7. The active matrix liquidcrystal display panel of claim 5, wherein said chalcogenide thresholdswitching material is an arsenic-tellurium based material.
 8. The activematrix liquid crystal display panel of claim 7, wherein saidchalcogenide threshold switching material additionally includes one ormore elements selected from the group consisting of germanium, silicon,phosphorus, sulfur and selenium.
 9. The active matrix liquid crystaldisplay panel of claim 8, wherein said chalcogenide threshold switchingmaterial is As₄₁ Te₃₉ Ge₅ Si₁₄ P₁, wherein the subscripts are the atomicratios of the respective elements.
 10. The active matrix liquid crystaldisplay panel of claim 8, wherein said chalcogenide threshold switchingmaterial is AS₃₈ Te₃₇ Ge₅ Si₁₄ P₁ Se₅, wherein the subscripts are theatomic ratios of the respective elements.
 11. The active matrix liquidcrystal display panel of claim 8, wherein said chalcogenide thresholdswitching material is As₃₆ Te₃₄ Ge₅ Si₁₄ P₁ Se₁₀, wherein the subscriptsare the atomic ratios of the respective elements.
 12. The active matrixliquid crystal display panel of claim 8, wherein said chalcogenidethreshold switching material is As₃₈ Te₃₇ Ge₅ Si₁₉ P₁, wherein thesubscripts are the atomic ratios of the respective elements.
 13. Theactive matrix liquid crystal display panel of claim 8, wherein saidchalcogenide threshold switching material is As₃₆ Te₃₄ Ge₅ Si₂₄ P₁,wherein the subscripts are the atomic ratios of the respective elements.14. The active matrix liquid crystal display panel of claim 1, whereinsaid Ovonic threshold switches are deposited onto glass substrates. 15.The active matrix liquid crystal display panel of claim 1, wherein saidOvonic threshold switches have an on current of about 1×10⁻³ A orgreater.
 16. The active matrix liquid crystal display panel of claim 1,wherein said Ovonic threshold switches have a threshold voltage as lowas about 3 volts.
 17. The active matrix liquid crystal display panel ofclaim 1, wherein said Ovonic threshold switches have a switching time ofless than about 1000 nanoseconds.
 18. The active matrix liquid crystaldisplay panel of claim 1, wherein said Ovonic threshold switches have across sectional area that allows for an aperture ratio of at least about0.6 or greater.
 19. The active matrix liquid crystal display panel ofclaim 1, wherein said Ovonic threshold switches are not sensitive tolight.
 20. The active matrix liquid crystal display panel of claim 1,wherein said Ovonic threshold switches are deposited at temperaturesbelow about 300° C. or less.
 21. The active matrix liquid crystaldisplay panel of claim 1, wherein said Ovonic threshold switches have ahold current of about 0.1 microamps, said resistive elements have aresistance of about 10⁷ ohms, and said liquid crystal display elementhas a capacitance of about 0.2 pF.
 22. An active matrix liquid crystaldisplay panel including:a plurality of liquid crystal display elementsdistributed in a matrix of rows and columns; means for supplying videosignals and display element selection signals, including row and columnconductors; and a plurality of paired Ovonic threshold switches andresistive elements each serially coupled between the corresponding rowor column conductor and the liquid crystal display element, said Ovonicthreshold switches active as display selection devices and currentisolation devices; wherein said Ovonic threshold switches have anoff-state resistance of at least 1×10⁹ ohms, and wherein said Ovonicthreshold switches include a body of chalcogenide threshold switchingmaterial disposed between two electrical contacts where saidchalcogenide threshold switching material is selected from the groupconsisting of As₄₁ Te₃₉ Ge₅ Si₁₄ P₁, As₃₈ Te₃₇ Ge₅ Si₁₄ P₁ Se₅, As₃₆Te₃₄ Ge₅ Si₁₄ P₁ Se₁₀, As₃₈ Te₃₇ Ge₅ Si₁₉ P₁, and As₃₆ Te₃₄ Ge₅ Si₂₄ P₁,where the subscripts are the atomic ratios of the respective elements.Please add the following claims.
 23. An active matrix liquid crystaldisplay panel including:a plurality of liquid crystal display elementsdistributed in a matrix of rows and columns; means for supplying videosignals and display element selection signals, including row and columnconductors; and a plurality of paired Ovonic threshold switches andresistive elements each serially coupled between the corresponding rowor column conductor and the liquid crystal display element, said Ovonicthreshold switches acting as display element selection devices andcurrent isolation devices; wherein said Ovonic threshold switches havean off-state resistance of at least 1×10⁹ ohms, and wherein said Ovonicthreshold switches include a body of chalcogenide threshold switchingmaterial disposed between two electrical contacts.
 24. The active matrixliquid crystal display panel of claim 23, wherein said body ofchalcogenide switching material is a thin-film.
 25. The active matrixliquid crystal display panel of claim 23, wherein said chalcogenidethreshold switching material is an arsenic-tellurium based material. 26.The active matrix liquid crystal display panel of claim 25, wherein saidchalcogenide threshold switching material additionally includes one ormore elements selected from the group consisting of germanium, silicon,phosphorus, sulfur, and selenium.